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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Positives and negatives of global warming

What the science says...

Climate Myth...

It's not bad
"Two thousand years of published human histories say that warm periods were good for people. It was the harsh, unstable Dark Ages and Little Ice Age that brought bigger storms, untimely frost, widespread famine and plagues of disease." (Dennis Avery)

Here’s a list of cause and effect relationships, showing that most climate change impacts will confer few or no benefits, but may do great harm at considerable cost.

Agriculture

While CO2 is essential for plant growth, all agriculture depends also on steady water supplies, and climate change is likely to disrupt those supplies through floods and droughts. It has been suggested that higher latitudes – Siberia, for example – may become productive due to global warming, but the soil in Arctic and bordering territories is very poor, and the amount of sunlight reaching the ground in summer will not change because it is governed by the tilt of the earth. Agriculture can also be disrupted by wildfires and changes in seasonal periodicity, which is already taking place, and changes to grasslands and water supplies could impact grazing and welfare of domestic livestock. Increased warming may also have a greater effect on countries whose climate is already near or at a temperature limit over which yields reduce or crops fail – in the tropics or sub-Sahara, for example.

Health

Warmer winters would mean fewer deaths, particularly among vulnerable groups like the aged. However, the same groups are also vulnerable to additional heat, and deaths attributable to heatwaves are expected to be approximately five times as great as winter deaths prevented. It is widely believed that warmer climes will encourage migration of disease-bearing insects like mosquitoes and malaria is already appearing in places it hasn’t been seen before.

Polar Melting

While the opening of a year-round ice free Arctic passage between the Atlantic and Pacific oceans would confer some commercial benefits, these are considerably outweighed by the negatives. Detrimental effects include loss of polar bear habitat and increased mobile ice hazards to shipping. The loss of ice albedo (the reflection of heat), causing the ocean to absorb more heat, is also a positive feedback; the warming waters increase glacier and Greenland ice cap melt, as well as raising the temperature of Arctic tundra, which then releases methane, a very potent greenhouse gas (methane is also released from the sea-bed, where it is trapped in ice-crystals called clathrates). Melting of the Antarctic ice shelves is predicted to add further to sea-level rise with no benefits accruing.

Ocean Acidification

A cause for considerable concern, there appear to be no benefits to the change in pH of the oceans. This process is caused by additional CO2 being absorbed in the water, and may have severe destabilising effects on the entire oceanic food-chain.

Melting Glaciers

The effects of glaciers melting are largely detrimental, the principle impact being that many millions of people (one-sixth of the world’s population) depend on fresh water supplied each year by natural spring melt and regrowth cycles and those water supplies – drinking water, agriculture – may fail.

Sea Level Rise

Many parts of the world are low-lying and will be severely affected by modest sea rises. Rice paddies are being inundated with salt water, which destroys the crops. Seawater is contaminating rivers as it mixes with fresh water further upstream, and aquifers are becoming polluted. Given that the IPCC did not include melt-water from the Greenland and Antarctic ice-caps due to uncertainties at that time, estimates of sea-level rise are feared to considerably underestimate the scale of the problem. There are no proposed benefits to sea-level rise.

Environmental

Positive effects of climate change may include greener rainforests and enhanced plant growth in the Amazon, increased vegitation in northern latitudes and possible increases in plankton biomass in some parts of the ocean. Negative responses may include further growth of oxygen poor ocean zones, contamination or exhaustion of fresh water, increased incidence of natural fires, extensive vegetation die-off due to droughts, increased risk of coral extinction, decline in global photoplankton, changes in migration patterns of birds and animals, changes in seasonal periodicity, disruption to food chains and species loss.

Economic

The economic impacts of climate change may be catastrophic, while there have been very few benefits projected at all. The Stern report made clear the overall pattern of economic distress, and while the specific numbers may be contested, the costs of climate change were far in excess of the costs of preventing it. Certain scenarios projected in the IPCC AR4 report would witness massive migration as low-lying countries were flooded. Disruptions to global trade, transport, energy supplies and labour markets, banking and finance, investment and insurance, would all wreak havoc on the stability of both developed and developing nations. Markets would endure increased volatility and institutional investors such as pension funds and insurance companies would experience considerable difficulty.

Developing countries, some of which are already embroiled in military conflict, may be drawn into larger and more protracted disputes over water, energy supplies or food, all of which may disrupt economic growth at a time when developing countries are beset by more egregious manifestations of climate change. It is widely accepted that the detrimental effects of climate change will be visited largely on the countries least equipped to adapt, socially or economically.

Comments

From the same (hardly scientific) article: “Since 2000, we’ve lost about 30 percent of the ice area as of 2009, but the thickness of at least the main glacier, the northern ice field, hasn’t changed a great deal. It was 50 meters thick then and now it’s on the order of 45 meters thick,” he said.

Lack of long-term data concerning the thickness of the glaciers is what undermined their forecast, Hardy said. “Before 2000, we had no reference for how to treat the thinning other than by looking at historical photographs.”

No cherry picking, as a matter of fact your posting goes to my point! When scientists don't have all the data or all the variables and they make forecasts based on that, then that disconnect is created.

Again this is not to say that global warming is not happening, or is not melting Kilimanjaro's ice, it just says that maybe there is a disconnect between currents trends vs. projections.

Joseph#152: By definition, a cherry pick is the use of a small subset of the available data, usually to draw a pre-conceived conclusion.

This is only a 'disconnect' for people who keep score based on who said what when. Those who understand the comment made by Hardy can see that such a prediction is justifiably updated by more complete analysis. This is the normal process of science or for that matter any predictive endeavor.

BTW, setting up a misrepresentation of another's argument so it can then be shown as a potential 'disconnect' is known as a strawman. In this case, 'they got the date the glacier would melt wrong' is a strawman. It is far more productive if we engage in substantial issues.

For some credibility, please pick a prediction from AR4 that you think is overstated (ie something with reputable science behind it).

Also, the statements about what is happening at this time are not full of doom & gloom. Furthermore 2 key ones (sealevel rise and arctic ice loss) show how conservative the predictions were.

What are the indicators that you would choose, that if went bad would make you say "OMG - I've been an idiot"? The two for me (currently doing okay but expected to go bad) would be world mortality and global grain production. The problem is that by the time you see a bad 10 year trend in these, a lot of people would have suffered. You want to wait till the house is burning down?

#150, 152 Joseph, we don't base our observations on a single glacier, see for example this post most glaciers worldwide are retreating and that trend is accelerating. Note John Cook's second-last sentence. A vast amount of information underpins the projections, and the tendency has been for the IPCC to err on the conservative side in their projections.

Every posting that rebutted mine that contained a single link to prove the poster's position was a cherrypick as well, but did anyone point that out? I didn't go to great lengths to find this article, it took me literally 1-2 minutes with a single google search to find this article. So it wasn't much of a cherrypick.

So you are saying it is a strawman because the substantive issue in the prediction is the melting of the glacier not so much the time it takes to melt??? So global warming of 1 deg over a decade is the same as global warming of 1 deg over a century?

Why shouldn't we keep score of the predictions as it relates to their timeline? And how is this not a substantive issue? I would say that us, (yes US!), AGW proponents have the obligations to keep score much less the willingness!

I would have expected you to say something to the effect that, yes Hardy messed up, but if you took all the predictions as a whole then the number of studies who got it right vs. the ones who got it wrong is 10-1, or something to that effect. Then I would have expected you to give me a link showing this (I would love to see this, btw).

That answer I would have respected, instead of brushing this off by this, "It is far more productive if we engage in substantial issues", i.e. "let's the change the subject" business.

If anything this answer just reinforces any reader's belief in a disconnect between the predictions and the current trends

The point was this: You found a single example that showed you what you wanted to hear -- and you generalized it to 'there's a disconnect!' That's the 2nd part of the definition of cherrypick I cited.

It is this logic that turns 'they got the weather wrong yesterday,' into 'they sure can't say anything about climate.'

"global warming of 1 deg over a decade is the same as global warming of 1 deg over a century?"

Your example was a glacier melting in a specific year vs another in the same decade or two. Please avoid these giant leaps from the small to the global.

This is not 'the science of predictions,' which we usually call 'climastrology.' There are no crystal balls or tea leaves in climate work. This is difficult science, worked by serious folks who see their every word picked over by self-appointed, self-taught and self-righteous critics - who hardly ever have to answer for their own words. Instead, the scientists often have their own words turned against them. BTW, have you applied your prediction-tester to Bastardi's cooling forecast? To Watts on this year's minimum Arctic sea ice extent? If you want to keep a prediction scorecard, please be sure to check both sides of the fence.

So yes, let's engage in more substantial issues. If you don't respect that, so be it. We'll let the readers decide on where the disconnect lies for themselves.

Muoncounter, I thought the whole idea of this website WAS to debate these very issues, instead what I am hearing from you is that I shouldn't question anything you say because it is "difficult science" and it's not "climastrology", and who am I to question them (or maybe I should say, "you"), because after all I am just a "self-appointed, self-taught and self-righteous critic"?!

You are correct in one assumption, I am not a scientist, but it is this website that invited debate from the general public (and aren't you a moderator on this site? you certainly act like it), but instead it seems to me more and more that criticism is not welcome on this site.

And as an FYI, no I am not going to apply a prediction tester to the other side, simply because the other side is non-scientific, and therefore their predictions have no credibility to start with.

I am out.

Response:

[DB] "I thought the whole idea of this website WAS to debate these very issues"

The goal of Skeptical Science is to explain what peer reviewed science has to say about global warming. While this site does invite discussion of the science, to characterize that discussion as a "debate" is to lend false credence/false equivalency to much of what comes out of the anti-science portion of the blogosphere (and traditional mass media, mores the pity).

Essentially, the basics of climate science and global warming are indeed "settled science"; what is being discussed in the literature today is how much warming we can expect, how fast we can expect it, and how bad things will get.

Joseph,
I simply objected to turning a thread that deals with a wide range of important topics (those bold paragraph headings in the original post) into a testing ground for various specific predictions. I don't know how you read that as 'I shouldn't question anything.'

Nor did I apply the words 'self-appointed' etc to anyone in particular. As to your claim that 'criticism is not welcome,' nothing could be further from the truth. However, criticism of what one person said is vastly different from a critical discussion of ideas. FYI, applying a critical eye to one side certainly looks one-sided, but that's just my opinion.

It is a shame that a call for a more substantial discussion should provoke such ire.

Eric the Red @160, the only debate which matters for the science is that which occurs in the peer reviewed literature. You, just as much as any other denier, are quite welcome to put your arguments into publishable form. That you are unwilling or unable to do so is a clear indication that your view point is not worthy of consideration by working scientists, and therefore not worthy of attention on a website whose stated purpose is to expound the published science of climate change. That you choose to 'debate' on the web when you clearly disagree with much published science, IMO, shows that you are not trying to learn the truth. If you where you would be trying to become involved in the debate that matters. Rather you are trying to persuade those who are ill informed on the topic in the full knowledge that you will be unable to persuade those who are well informed.

EtR. There is certainly a lot under debate in climate science, but the basics (Temp is increasing, CO2 is a greenhouse gas, CO2 is increasing, humans are responsible) are in fact "settled science." By that I mean that no one in the scientific community thinks these are interesting problems anymore. The evidence behind those propositions is just too compelling. It has been for decades now.

Also, let's be honest. This forum does not constitute a true debate on the scientific matters. To be part of the real scientific debate, we would actually have to be doing original research and actively publishing that research in peer reviewed journals, not just posting to blogs on the web. To be part of the scientific debate requires that we be informed and capable enough to convince other well informed and capable people that we have something substantial to contribute.

People feel annoyed by this state of affairs, I guess because they feel like decisions are being made that affect them without their having a say. Of course, they might feel more annoyed if they were actually forced to go through the training needed to allow them to participate in the scientific debate!

More pertinently though, this resentment is misguided. The only decisions that are being within the scientific community are with respect to what the evidence says about how the world works and our place in it. What we actually do as a society will have to be a much more public decision because that involves taking values into account. Without scientfic evidence, you can't have rational decision making -- it becomes impossible to determine whether any action actually serves the values it is intended to serve.

Hello, I'm a newcomer in this field. I have read most of the arguments on all sides. This site by the way is really good. Keep up the god work

The point of my question here is - OK, AGW is real, but for policy and decision makers, how much confidence can be placed in IPCC predictions, and how much weight should we attach to them?

[- inflammatory comment snipped-]

It would be great if any replies could be objective, rather than emotive.

Response: (Rob P) Please take heed of the advice in your last sentence. Make sure posts adhere to the comments policy. If you wish to re-frame your question this SkS post is the relevant thread to comment on: Is the IPCC alarmist?

I have visited Tuvalu. The situation there is terrible. They had a very traditional lifestyle and are really friendly people. I still have two grass hula skirts they gave me. The people there have few options besides migration. Your link says that Australia turned down a Tuvaluan proposal for migration. Who will take them in? Increased waves from stronger storms (caused by AGW) have combined with sea level rise to poison most of their fresh water.

Your link says Samoa is also rationing water. Samoa is a much larger country with much greater land mass. It must be a serious drought for Samoa to be running short of water.

Regarding the entries about western tree mortality, pine beetles under the Environment negatives in the Intermediate tab, I quote from a blog post by a fellow I've known for more than forty years. This is not peer-reviewed science, but I think it reflects a human perspective on those environmental negatives (the ellipses in the post are his, and I have omitted nothing):

"I got lost in the details of travel and the hassle of finding places to work on the blog/sort pictures and talk about the travels. The massive environmental upheaval caused by global warming in the pine and spruce forest of Idaho and Montana is stunning. The forest is dieing. Pine Beetle and Spruce Moths are unchecked by the long frosts of winter. The result is hundreds perhaps thousands square miles of dead and dieing forests. There is the loss of the wood and timber...the water holding of the trees, the air purification, the oxygen generation but, more.... The millions of pine and spruce needles in the waters have changed the PH of the lakes and streams. The water born insect life is gone. Three different streams, three hoops set out for three days each ... less than 20 insects collected where there should have been thousands. Breeding salmon seen but no fry, no first or second year fish, no trout, no white fish, no suckers...the streams are dead.

"Sorry my mind is still struggling with the facts and unsure as to how I will deal with those who say my truth is lies. Will they come walk the streams, roll the rocks, hang the hoops, count the insects, float the rivers and prove me wrong or will they simply move their mouths in denial? I was unable to write this last summer and do not know what I can do this year."

"As extreme weather events such as drought and flooding become more common, protecting the nation's main wheat producing areas grows in urgency - thus the first regional program chose the northeastern parts of the country,..."

Under "Sea Level Rise" it would be good to specifically mention coastal erosion. Rising sea level threatens not just those who will find themselves beneath the waves, it also threatens those atop the tall cliffs.

Basically rising sea level changes the mass balance of sediment on beaches. By creating new room ("accommodation space") for sediment storage, sea level rise can quickly drain a beach of sediment, exposing the surface protected by the beach. Also it obviously provides more ready access for storm waves to the base of erosional bluffs.

To better understand the messy nature of marine transgression during sea level rise, one could look to areas where subsidence has simulated this effect such as on the Mississippi delta (size warning - 2 mb pdf):

I don't know of a nice paper that looks at cases like this and uses it as an analogy for climate-change related sea level rise.

Interesting article, thanks for the mental meal! A couple of questions:
I'm in Australia - will we get *fewer* droughts as a result of global warming? (Thanks for the video link @muoncounter, was awesome). It's kinda important, given we've got a carbon tax as the current political football. Also, can it be predicted *when* (ie which season) increases/decreases in rain will occur? The true nightmare in OZ is a wet spring followed by a hot summer, as that means insane bushfires. However a dry spring/wet summer is awesome. Makes a huge difference!
- What about refugees? How many millions of people are going to have to move? That's going to create a huge cost, surely.
- Finally...ok, this one's creepy, but I have to ask. If (i) it's true that most human genetic diversity is in Africa, and (ii) Africa gets it in the neck, are we going to lose great wodges of genes that could be used for treating inherited diseases etc? I don't mean to treat people as harvestable cattle, but if it is a genetic loss, and pointing out the loss can reduce the likelihood of them being left to die, then it needs to be said...

I bet this has already been metioned, but what happens when the ice caps melt? Wouldn't high up northern places become habitable? How about the deserts , which will border the oceans, creating new forests for all. And most of all, wouldn't it be great for microorganisms (especially Archea) to live, therefore giving us new lifeforms that take the place of the old niche of the old lifeform

ShadedX, the problem is that even if temperatures, say, in northern Canada or Siberia became suitable for growing wheat or whatever, or if it starts raining regularly in somewhere currently desertified (not generally forecast, but lets imagine for a moment)... you will not develop the soils required to sustain agriculture or forestry for many hundreds or more likely thousands of years. Soil development (pedogenesis) is a very slow process - a good example is the vegetation successions you see after ice retreat at the end of past glaciations - trees only thrive thousands of years after the first colonising grasses and shrubs.

Reiterating skywatcher - its not whether warming is better or worse, but the rate at which change occurs. Rapid change (and this is very rapid change in geological terms) is associated with mass-extinctions. I doubt very much that humans would go extinct but the disruption to our agriculture will be very considerable. The question to ask is with the cost of mitigation is less than the cost of adaption. Studies so far say better to mitigate.

Did anyone else cringe reading this one:
===
Melting Glaciers
The effects of glaciers melting are largely detrimental, the principle impact being that many millions of people (one-sixth of the world’s population) depend on fresh water supplied each year by natural spring melt and regrowth cycles and those water supplies – drinking water, agriculture – may fail.
===

1) One-sixth of the world's population is not just many millions but at least a billion.

2) While I could believe a billion people are dependent on rainwater runoff, or spring runoff from melting snow that fell during the winter, where exactly are there a billion people in the world depending on water from actual glaciers?

If global warming was somehow able to stop rain, or prevent snow from falling every year, I could see that being a problem for a billion people or more. As far I know (though I'm admittedly quite ignorant on the subject) reduced global precipitation hasn't been proven as a result of AGW yet. Has it?

This statement seems takes an easily observable phenomenon (glaciers shrinking) that the general public can understand, and associate it *incorrectly* with catastrophic results. It's this attitude of alarming the public with misleading claims that make me skeptical of AGW reporting accuracy in general.

mohyla @174 - "reduced global precipitation hasn't been proven as a result of AGW yet. Has it?"

No. Global precipitation is expected to increase with global warming - it appears to have done so in ancient "greenhouse" periods much warmer than today. So there is an observational basis to support the modeling too.

The problem being that it (precipitation) won't fall in some areas where humans have set up large tracts of agriculture. A compounding problem is the precipitation is likely to fall in heavier, but less frequent, downpours. Again a significant problem for agriculture.

This excludes several minor rivers flowing into arid regions with lower population density:

Glaciers act as natural dams, absorbing large precipitation events while maintaining a relatively steady flow of melt water. As such, they help prevent floods, and prevent seasonal water shortages. Consequently your skepticism is in this case at least unwarranted.

How dependent the various rivers are on melt water varies substantially, ranging from 60% for the Indus river to 10% for the Huang He and Yangtze. As such, loss of the water flow buffer from glacial melts would only effect people relying on the Yangtze or Huang He on very wet (flood) or very dry (drought years), whereas on the Indus, adverse impacts could be expected every year. Further, because glacial melt is not the only impact of global warming, the overall effects on different rivers can be quite different. The primarily rainfall dependent Chinese rivers, for example, are expected to increase average flows by about 10%, while the Brahmaputra (a major tributary of the Ganges) is expected to reduce average annual flows by about 20%. (Note these are annual figures, and do not address the issue of changes of timing of river flows.)

JMurphy: Maybe I'm splitting hairs here, but the misleading part is that the paragraph title is "melting glaciers" but the 1/6 of the world's population figure seems to be referring to the number of people living in a "snowmelt-dominated, low-reservoir-storage" area. Glaciers and annual snowfall are quite different things but Barnett seems to ignore the difference. The Barnett paper says of the Himalaya–Hindu Kush region:

"...there is little doubt that melting glaciers provide a key source of water for the region in the summer months: as much as 70% of the summer ﬂow in the Ganges and 50–60% of the ﬂow in other major rivers."

After checking the three sources for these figures, I find this claim to be very misleading! Allow me to present the relevant sections of Barnett's sources:

Singh, Bengtsson:
"Reduction of water availability during the summer period, which contributes about 60% to the annual flow..."
Careful reading reveals that this source does not say glaciers contribute 60% of the total water flow in the river, but rather that the water flowing in the summer period (a combination of rain, glacier melt and snow melt) is 60% of the annual total. From this we can deduce that glacier melt itself is only a fraction of 60% of annual flow, not a full 60%.

Singh, Jain, Kumar:
"The snow-covered area in the basin was determined using satellite imagery. It is observed that, on average, about 70% of the area of the basin is covered with snow in March/April and this is reduced to about 24% in September/October. The average snow and glacier runoff contribution to the annual flow of the Chenab River at Akhnoor is estimated to be about 49 percent."
They do not claim 49% is from glaciers, but a combination of snow and glaciers, so for Barnett to use this figure when talking about glaciers alone is inaccurate. Also, it appears there is still snow cover in this basin into October, so presumably it would be there all year. The importance of this is that, in a glacierless basin, there would still be plenty of snow melting every year to replenish the river. The actual fraction by which river flow would be lowered without the glaciers is not explained here (?) but it certainly is not 50%.

Singh, Kain:
"It was found that the average contribution of snow and glacier runoff in the annual flow of the Satluj River at Bhakra Dam is about 59%..."
Once again, snow and glacier runoff is lumped together. As snow is an annually replenished resource whereas a retreating glacier is a more irreversible change, it would be helpful to know the separate contributions of each. For Barnett to use the full 59% in his paper, he is actually talking about a scenario where not only are the glaciers gone, but it never snows anymore either!

Sorry, I can't comment on the Immerzeel paper as I can only read the abstract and there is nothing specific to the Barnett paper in it. But I hope you'll agree, that Barnett's paper is misleading and a misrepresentation of data.

logicman: Good point. However, I'm not arguing that glaciers aren't shrinking or won't continue to shrink. I'm just curious where the evidence is that *so many* people are dependent on the actual water melting off glaciers in the first place instead of other sources like snowmelt or rain runoff.

Tom Curtis: I do like your phrase "partially dependent". This seems a much more reasonable way to describe the situation. Do you know if there have been any studies in at-risk areas to determine how much meltwater actually comes from glaciers in the summer vs. remaining snowpack from the previous winter? It seems this would be valuable information.

"Glaciers act as natural dams..." which can burst causing massive flooding events downstream. A retreating glacier would eliminate this possible threat, so it's not all bad news.

"...absorbing large precipitation events..." I don't understand what you're referring to here: rain or snow? Does a glacier have a way of absorbing rainwater besides damming it up? logicman just told me rain cannot add to the mass of a glacier, so I'm confused now. If it's snow, why would a glacier need to absorb this? Is snow just accumulating on the ground more of a danger?

"...while maintaining a relatively steady flow of melt water." Melting snow would also provide this, but in areas where the snow melts away quickly, glaciers would definitely provide a more permanent source of water. I agree with you on this point. I just wonder how significant this percentage is compared to snowmelt in those at-risk areas.

KR: I see. Declining snow extent seems a natural result of a warming planet so I'm not surprised. My original post was not an argument that warming isn't happening, just that the figures presented there seemed exaggerated in reference to "melting glaciers".

Anyone would need to be very sceptical of your claims, especially (with regard to Singh & Bengtsson) when you previously claimed "[c]areful reading" of that source allowed you to "deduce that glacier melt itself is only a fraction of 60% of annual flow, not a full 60%."
Who claimed it to be "a full 60%" ?

With regard to that "fraction", how have you worked out that fraction ?

Under warmer climate, a typical feature of the study basin was found to be reduction in melt from the lower part of the basin owing to a reduction in snow covered area and shortening of the summer melting season, and, in contrast, an increase in the melt from the glacierized part owing to larger melt and an extended ablation period. Thus, on the basin scale, reduction in melt from the lower part was counteracted by the increase from melt from upper part of the basin, resulting in a decrease in the magnitude of change in annual melt runoff.

I.E. Less from snow and more from the glaciers, leading to decrease in magnitude of annual change - in no way misleading or wrong with regard to Barnett et al's claim : "...but there is little doubt that melting glaciers provide a key source of water for the region in the summer months: as much as 70% of the summer flow in the Ganges and 50–60% of the flow in other major rivers."
(My bold)

If you still think that is misleading, provide the evidence for a figure you think is more valid, i.e. under 50%.

JMurphy:
The abstracts are all I had access to, and I apologize for any misunderstanding. The figures are already present in the abstracts though, so I would still consider my statement valid.

I'm going to ignore the quotation you pasted in from the abstract because it does not mention percentages at all and it's the percentages that I said Barnett must have got wrong.

Once again, the relevant sentence from the abstract is:
"Reduction of water availability during the summer period, which contributes about 60% to the annual flow, may have severe implications on the water resources of the region..."

Here we have an actual figure, 60%. The way I read this sentence is that there may be water flowing all year in this river, but the *water* from the summer period specifically represents 60% of the annual flow; i.e. the water from fall, winter and spring together makes up only 40% of the annual total. Do you agree with my analysis of this sentence? If not, please ignore the paragraphs below and clarify how I read this sentence wrong.

Now if *all* the water flowing in the river in the summer period came from melting glaciers, this would mean that 60% of the annual flow does indeed come from glaciers, since the summer water accounts for 60% of the annual flow. However, I made the reasonable (wouldn't you say?) presumption that the summer flow does not only come from glacier melt, but also snow melt and rainfall.

If you agree with my presumption, then you would agree only a fraction of the summer flow is from actual glacier melt, which means only a fraction of 60% of the annual flow is from glaciers. That's how I arrived at this "fraction" and I stand by my previous statement.

How big is the fraction from glaciers? If 5/6 of summer runoff comes from glaciers (that seems pretty generous, but without further evidence I admit it's possible) then Barnett would still be OK using a figure of 50%, but any less and Barnett's figure wouldn't be accurate. Without searching the full text of the paper for a percentage for glacier melt specifically, we have no way of proving or disproving this. Considering his sloppy use of the other 2 sources, I don't have much confidence in his referencing of this source either.

If you have access to the full text, by all means let me know if there is a figure for glacier melt specifically. If not, we'll just have to leave a question mark on this one.

However, I'll take your lack of comment on the other 2 sources as agreement that Barnett's misrepresented the data in saying that "melting glaciers provide....50-60% of the flow" in these rivers. It is not melting glaciers alone, but the combination of melting glaciers and melting snowpack.

So, you don't know what the actual relevant percentage is but you still feel justified in making your original accusation anyway, because of your reading of the other two abstracts. I'm sorry but that is not the sign of someone who wants to discover the truth, but someone who has already made their mind up and will not change it, no matter what. How can anyone confidently make the accusations you have without first checking whether there was at least some justification in what you are claiming ?

I have to say 'What is the point ?' It would appear that you are not here to discuss, but only to make baseless accusations and to stick to your beliefs come what may.
I have read exactly the same abstracts as you have but I know that only reading the full papers will give the answers to any queries you might have. I also have confidence that those who have produced all the papers referred to did so using figures that have been checked and confirmed by others.
Until you have proof otherwise, I suggest you withdraw your accusations.

JMurphy: I think you may be over-reacting to mohyla103. Questions raised are reasonable, and are still valid based on info reported in the abstracts. Remember, those of us outside of the paywall don't always have free access to the entire paper. Also, mohyla103 reacts reasonable to KRs evidence presented @182, suggesting motives are in line with seeking the truth.

1. Negative economic impact is more likely for temperature increase exceeding 2 degrees C (minimum estimated in IPCC AR4 for year 2100). See figure 1 in the paper.

2. Table 2 shows estimated carbon taxes (per metric ton) that would compensate for the expected future economic loss. In Tol's words: "The best available knowledge—which is not very good—is given in Table 2. A government that uses the same 3 percent discount rate for climate change as for other decisions should levy a carbon tax of $25 per metric ton of carbon (modal value) to $50/tC (mean value). A higher tax can be justified by an appeal to the high level of risk, especially of very negative outcomes, not captured in the standard estimates (Weitzman, forthcoming)."

MarkOhio, I did not intend to over-react but if it is seen in that way then I apologise to mohyla103 for giving that impression, and hope I haven't scared him/her away !
However, I still think it excessive to make the four accusations I quoted in my previous post, without the required solid evidence to back them up. At least, I don't see the abstracts as containing such solid evidence, anyway. And I'm not saying that the accusations are necessarily definitely wrong - just unproven and, so far, carelessly made, in my opinion.

I don't understand why you would say "what's the point". Saying that it "would appear that [I am] not here to discuss, but only to make baseless accusations and to stick to [my] beliefs come what may" is not only rude but is also baseless and should be withdrawn.

I *still* stand by my claim. Here is the HARD EVIDENCE which you have requested but, even though I presented it above, you have not yet confronted:

The Singh, Jain, Kumar paper's abstract states "The average snow and glacier runoff contribution to the annual flow of the Chenab River at Akhnoor is estimated to be about 49 percent."

It doesn't really matter what the rest of the paper says, the abstract already tells me that snow and glacier melt together make up less than 50 percent of the flow in this river. There's no way the paper can have any figure higher than 49 percent for glacial melt alone... unless snowmelt somehow imparts a negative amount of water to the river.

Also, unless snow melt accounts for 0% of the flow in the river, the amount from glaciers MUST be even less than 49%. So for Barnett to cite this source as evidence for a 50-60% glacial melt contribution is in fact WRONG. Please acknowledge this or I will have to believe it is you who is going to stick to his beliefs come what may.

Considering he definitely misrepresented data from at least this source, wouldn't you think it reasonable to examine the other sources more closely as similar errors are likely? Apparently peer review completely missed the error in Barnett citing this source, which is why I don't have the same "confidence that those who have produced all the papers referred to did so using figures that have been checked and confirmed by others" like you do.

In light of recent discussion, I will restate my position:

1. "misleading claims that make me skeptical of AGW reporting accuracy in general;" I stand by this, as Barnett's use of data has been proven to be wrong in at least one case. Notice I said skeptical of "AGW reporting" not "AGW itself". It's the exaggerations in reporting that irritate me.

2. "Glaciers and annual snowfall are quite different things but Barnett seems to ignore the difference.;" I can rephrase this as "Barnett seems to ignore the difference in citing at least one paper, where he cited a 49% for combined glacier and snow melt figure as evidence for 50-60% contribution from glacial melt alone".

3. "After checking the three sources for these figures, I find this claim to be very misleading!" can be rephrased as "After checking the abstracts of these three sources, I find Barnett's claim to be misleading. At least one abstract proves Barnett misrepresented the data, so careful examination of the other 2 sources is definitely warranted."

4. "But I hope you'll agree, that Barnett's paper is misleading and a misrepresentation of data." can be rephrased as "But I hope you'll agree that the figures in this part of Barnett's paper are misleading and a misrepresentation of data."

What is the maximum percentage possible ? How much of that maximum is contributed by glacier-melt?
Admittedly more than 49% from glacier and snowpack melt is possible at a peak time of the year. Admittedly, the amount from glacier melt could at a peak time exceed 49% of the flow in the river. However, this is irrelevant as Barnett never made this claim. See below.

Your 2nd question: When does that maximum occur ?
I don't know. However, this is irrelevant as Barnett's original 50-60% did not refer to peak flow at a certain time of year but total flow. Were this the Ganges, I could understand your point as Barnett specifically referred to the summer period for the Ganges. However, for the Chenab river, he did not.

As far as I can tell, Barnett was not talking about some peak melting time where glacier and snowpack melt contribute more to the river than usual, he was talking about their total contribution to river flow; therefore, an average yearly figure is what would be required as evidence, not a figure about a period of peak contribution. Maybe this is where our misunderstanding lies?

"Glaciers act as natural dams..." which can burst causing massive flooding events downstream. A retreating glacier would eliminate this possible threat, so it's not all bad news.

Erm, no.

No, no, and NO.

Glaciers do not impound water, they hold it as frozen mass, so there is no equivalency with "bursting" dams.

However...

If precipitation falls as water when it would previously have fallen as snow, then there will be greater downstream flows during precipitation seasons. This may indeed cause flooding, but not of the instantaneous sort that follows a dam bursting.

Therefore a "retreating" glacier will more likely cause flooding events, but not in a manner akin to a bursting dam.

It also means that there will be reduced (or no) flow during non-precipitation seasons.

mohyla103 wrote : "As far as I can tell, Barnett was not talking about some peak melting time where glacier and snowpack melt contribute more to the river than usual, he was talking about their total contribution to river flow; therefore, an average yearly figure is what would be required as evidence, not a figure about a period of peak contribution. Maybe this is where our misunderstanding lies?"

The misunderstanding would be dependent on whether you were referring to this statement in Barnett et al :

The hydrological cycle of the region is complicated by the Asian monsoon, but there is little doubt that melting glaciers provide a key source of water for the region in the summer months: as much as 70% of the summer flow in the Ganges and 50–60% of the flow in other major rivers 40,41,42.
(40. Singh, P. & Bengtsson, L. Hydrological sensitivity of a large Himalayan basin to climate change. Hydrol. Process. 18, 2363–-2385 (2004).
41. Singh, P., Jain, S. K. & Kumar, N. Estimation of snow and glacier-melt contribution to the Chenab River, Western Himalaya. Mount. Res. Develop.
17(1), 49–-56 (1997).
42. Singh, P. & Jain, S. K. Snow and glacier melt in the Satluj River at Bhakdra Dam in the western Himalayan region. Hydrol. Sci. J. 47, 93–-106 (2002).)

If so, he mentions "summer months" and "summer flow" (peak melting time, perhaps ?); references the Chenab river, and writes "as much as...50-60%...".

Which part of Barnett, specifically, were you referring to - particularly with regard to those particular references ?

Yes, that's exactly the sentence I'm referring to. The wording here is tricky, so this is probably where the misunderstanding comes from. I find it strange that he mentioned summer months, then specifically referred to "summer flow" with the Ganges, but not with other major rivers. So I interpret this sentence like this:

"a key source of water for the region in the summer months"
Glacier meltwater provides water in the summer for the Ganges and other major rivers. The sources all confirm this as well.

"as much as 70% of the summer flow in the Ganges"
This one's straightforward. The abstracts of Barnett's sources don't mention this but I presume this figure is in the full text and I'm not arguing anything here.

"and 50-60% of the flow in other major rivers"
What flow is he talking about? I interpret this as a yearly average, not summer specifically, especially since the sources all mention a yearly average figure around 50-60% right in their abstracts. Notice Barnett did not say "summer flow" like he did with the Ganges. Obviously, glaciers do provide water "in the summer months", so Barnett is not wrong to word the first part of his sentence this way, but I don't think you can assume this 50-60% figure actually refers to summer flow.

I'm working on getting access to the full text of the Singh, Jain, Kumar paper and I'll let you know what it says in there as soon as I find out.

Did you mean that glaciers can be actual dams that hold liquid water back behind them, or that glaciers act like a dam in that they hold precipitation (snow, not rain) at a higher altitude? If it is the latter, then I misunderstood the phrase "natural dam" in your original statement.

I thought you were referring to something like this, where a glacier acts as a true dam, actually impounding water, and actually bursting:
http://en.wikipedia.org/wiki/Glacial_lake_outburst_flood

As expected, there is no mention whatsoever of glacial melt separate from snow melt. In this study, they were calculated together and, in fact, not even directly measured. FYI the study was completed with data collected over 10 years, so the figures presented are averages. Nowhere in the paper does it give a "maximum percentage possible" that you had asked about, so for Barnett's figures to be referring to that isn't possible. Here's one relevant section, from page 52, showing that the author of this paper did not distinguish between glacial melt and snow melt in this study:

"Snow and glacier contribution to the 10 years' volume of flow in the Chenab River at Akhnoor has been estimated using the following water balance approach:

Barnett was definitely correct to cite this paper in saying that glaciers provide a key source of water in the summer, of course. Page 51: "In the post-monsoon season, flow is believed to be from the glaciers and occasional rainfall events in the basin. In general, glacier contribution starts in June/July and continues until September/October." But that's all it says. There are no percentages given here for glacial melt.

There is a table on page 51 showing the "Average quarterly distribution of annual flows" where we learn that the water flowing in the July-Sept period represents 51.1% of the annual flow. However, this is once again not referring to glacial melt alone, as flow in the July-Sept period comes from rain, glaciers and snow. Singh et al. confirm this in the discussion below the table where they say "[t]he higher contribution to the annual flow from the pre-monsoon season (April-June) and the monsoon season (July-September) is due to the combination of rain, and snow and glacier-melt runoff."

One more relevant bit, from the Conclusion section on page 56:

"2. It was found that snow and glacier-melt runoff contribute significantly to the total runoff of the Chenab River at Akhnoor. Based on 10 years of data analysis, the average snow and glacier-melt contribution to the annual flow of Chenab at Akhnoor was found to be 49.10 percent. The remainder is contributed by rainfall."

In conclusion, Barnett was wrong to cite this paper as evidence that glaciers contribute 50-60% of the flow in this river, either for the summer or a yearly average. It is actually glacier and snow melt together (and technically it's not 50 it's 49). The peer-review process missed this error. Please acknowledge this, as I am no longer arguing based on incomplete information.

Considering the same kind of wording and figures appear in the abstracts of the other 2 papers cited by Barnett for this claim, I strongly suspect he and the reviewers committed the same error there.

To Barnett's credit, the summary at the beginning of the article actually does mention snowpack and glaciers, not just glaciers alone.

You write: Health negatives. Spread in mosquite-borne diseases such as Malaria and Dengue Fever.

The article you quote (Epstein et al. 1998) states: "the minimum temperature for P. falciparum malaria parasite development is experimentally between 16° and 19°C and varies among mosquito species (Molineaux 1988). In general, isotherms present boundary conditions, and transmission is generally limited by the 16°C winter isotherm."

This is simply wrong: malaria was endemic in Canada less than 100 years ago. A recent Canadian editorial (reference and quote below) quotes several old medical articles on this subject. The recent recurrence of malaria in developed countries is entirely due to increased air travels and drug-resistant Plasmodium. It has nothing to do with climate change.

"Malaria is an old Canadian disease. It was an important cause of illness and death in the past century in Upper and Lower Canada and out into the Prairies.1,2 During the period 1826–1832, malaria epidemics halted the construction of the Rideau Canal between Ottawa and Kingston, Ont., during several consecutive summers, with infection rates of up to 60% and death rates of 4% among the labourers.3 Malaria also appears to have had an important effect on the health of the Northwest Mounted Police in the Prairies.1 When the Montreal General Hospital opened, in 1823, 3% of the first 3665 patients admitted were ill with malaria, and 3% died in hospital as a consequence. Canada’s own William Osler popularized the use of the microscope for the diagnosis of malaria in North America in the late 19th century.4 The endemic malaria in North America was probably reinforced each spring by waves of infected immigrants from Europe. Several of our indigenous Anopheles mosquitoes were, and still are, capable vectors of human plasmodia."